Drill mechanism



Allg. 28, 1945. w w PAGET 2,383,499

1 DRILL MECHANISM Filed Maron 2, 1942 2 sheets-sheet 1 Aug. 28, 1945. w. w. PAGET DRILL MECHANISM Filed Marchy 2, 1942 2 Sheets-Sheet 2' I@ J a?? @y w ai Patented Aug. 2s, 1945 l .DamLfMECHANIsM i" 4virili wager, Michigan oily, 41nd-, assigner tof 1SullivanMachineryCompanhia; corporation of :Massachusetts lipplipazionmafcn 2, 194g, Ise r ial 1 \i0. 432,951 is claims. (01.255-45) MyV invention relates lo drill mechanisms, and

more particularly to feed control in echanisrnsnoithe rotarytype.` In the t drilling ofmaterialbyineansof rmeoiis fondelli i i @rotary type drill, it `is Adesirable that the drilling' tool be subjected-to o: continuous Afeeding:pre ssurel in :order that the maximum-.eliwncymay beobtained. I txis als` o d 'esirabletoavoidlasirbjeotionpf the drill mecha iovsliddeneclianees infloedfol' o drin: ngloflthe Millington! against en excessive Je: distance to whiohma'y' Icanselithe tool to h egdaznagedf- *i g ley nrovidingmeens for vieldingly ffeedilie drillinegtool .toward Lits Werl: .at pressures maylbeincreaed until th of the drillirisltoolireaoh value, and thenprevcntinefu'rther increase inthe feeding .plessureuutil the -resistanee oroi'here Will betlohieineda V drill mechenismlvvliich operates hielef'ieilciesloutzisneYer-subleeled toexoeissivloede?" g Anpbiect of myiriventionis lemmi/ ideen Pro ed drillmeclianismlof,the rotary-type Anoihe obliegt 'iste providein aririllmeohanisropf inc rotaivllylle ,improved mee-ns :for controlling tice. l

Injthesedrawingsz i i Fie- `1 `is anion view of ad1 ii 1l mechanism-:herr

Y "Figi-"2 :isra side .elevational View, .Withpartsbroli Fig.' Sigan-enlarged lungi dinal verticalsecr- V "Fig-*rise verticaleioss sec orielviewtalien on planelof'lifig. 3 and showingla :modication ofithe feed control means. v 1

,Fig. .7.is across sectional viewtkenfon therline 1T1pfr31g 6 t l=In` the. drawngs,there is f showna ,drill `mechanism, .generally designated l fooinprising afpow'er unit L2 -arranged -to .rotate al drilling tool -3 Vand mounted for`reiproeation,on Vasupp or-tingand l neenefaheiarilimglooihaseecreeseoSomewhere; t

guiding shellil. -A feed mechanismfgenerally designatedzE, is provided for feeding thepowerunit along .the supporting andgllidng frame ,'relaf tive tothe work. l

The powerunit 2 ,isshown ,herein as @n e1eetriemotor 6 having a easing'. Bia-ndvfrpnt andirear rrnotorheads Sand il) secured to .the .en dsof Vthe casingas by tie Abolts .IJ. Arranged withinthe motor casing isaistationaryi-ield Winding l2 .and an armature rotorsl ifixed to .la .powerfshaft ,I E, as bylakey I6. The power, shaftisrotatablysupported in thefront and rear Inotorheads byfbear.- ings I 'l' and le, y and has `xed to its forward end a chuck 2llforre o 'eiv i ng the drilling tool 3. Formed integrally with the rearinotor head I O is ,a rear.- Wardly extendingl rprm'ection .,Zl rotatably supported in bearings-22 .carried bylareelzheadblock 23. The inner races lof the bearings T22 ,are clamped bete/ eene sholllderl Qn theprojeetion 2| and an vr annular rnember'-2 attachedto the rear end of thepiroiectioxil Las byzbolts ,2v-l. The outer races ofotheloe rings .22 are held securely within an annular recess in therear head-block by alring attached tovthefheadfhlook Iby bolts l29. `The projecticnll is held, by n1e,ans which will be shortly describerd, againstrotation the bearings 22 during norrnailoadsnihe motor, but iS Permitted ioliiirn slightly-at a predetermnedrnaximnni loaden the motoripreiecting a controlofthefeeding ofthelatter'.` Cleansing liquid is siimolied lhrolleh .o `oonriection ,313' yurl olel the control of a mannally Operated valve 3| tn a passage :32 extending 4tliroilfell the ,heed block 2.3 into communication with a lignidsunplyinb'e232e extending through the power shaft l5 and through which liquid is subpliedpn 'its wey@ bhenruiing tool 3 and to thebottinof-the drill hole.

The rear head b1ockf23 is provided, as SllQWn in Fig. 4,vvith laterallylprojecting flanges 3,3 tting Within. guideways'34 infa -troughliknefportion or member `35 `oi` the supporting and'guiding shell 4.

the front and rear ends of the member 35. Any suitable means. such as an operating handle 4|, may be provided for rotating the feed screw 31. Formed integrally with the troughlike member 35 is a projecting portion 42 adapted to be clamped in a suitable mounting for holding the member 35 in the desired drill-supporting position. Arranged within the-bosslike portion 36 1s a feed nut 43 threadedly engaging the feed screw 31,'and having grooves 44 in its outer surface extending in the same direction as the feed screw, and receiving flanges 45 on the portion 36. The ,l

flanges 45 have a sliding flt within the grooves 44 so that the feed nut and the rear`l head block,

may move relative to each otherlongitudin'ally of the feed screw but are held against relative angularmovement. A nut 46 isthreaded upon the reduced forward end of the feed nut and is engageable with the forward end of the bosslike portion 36 for limiting lthe rearward movement of the feed nut relative to the rear head block. A lock nui'l 41 threaded on the front end of the feed nut holds'the nut 46 in position. VThe rear end of the feed nut is provided with an enlarged head 48 fitting loosely within a chamber 49 in the depending portion 36. Arranged within the chamber 49 is a coiled spring 50 surrounding the body of the feed nut and acting against the front end wall of the chamber 49 and the inner surface of the head 48 on thek feed nut for urging the latter to the right, as viewed in Fig. 3.

In order to feed the drill relative to its work it is only necessary to rotate the feed screw 31 so as to cause the feed nut 43 to travel along the feed screw. As the feed nut is caused to travel forwardly along the feed screw, the enlarged head 48 on the feed nut acts against the spring 50 and forces the latter against the wall 5| for moving the rear head block 23 along the member 35 toward the work. To prevent an increase in the forward feeding pressure on the drill when the load on the drill motor reaches a predetermined maximum value there is provided a locking mechanism, generally designated 54, for locking the feed screw 31 against rotation. Itwill be seen that when the feed screw is locked against rotation, the spring 5|] will continue to urge the drill motor' forwardly but with a gradually decreasing feeding pressure as the drilling tool cuts itsway into the material. When the resistance to rotation of the drilling tool is reduced somewhat, the locking mechanism 54 releases the feed screw so that the latter may be rotated for effecting forward movement 4of the feed nut to build up vthe feeding pressure again. The drill is fed rearwardly along the guide member 35 by rotating the feed screw in a direction to cause the feed nut 43 to travel rearwardly along the screw. When the nut 46 on the forward end of .the feed nut engages the frontend of the depending portion 36, the head block 23 with the drill motor attached is moved rearward- 1y along the guide member on continued rear.

ward movement of thefeed nut.

The locking mechanism 54 is adapted to be actuated by a rotary movement of the drill motor casing relative to the rear head block 23. This locking mechanism comprises, as shown in Figs. 3 and 4, a latch 55 arranged within a chamber 56 in the head block `23 and pivotally mounted between its ends on a pin 51. The pin 51 extends through the chamber parallel tothe feed screw and is supported 'at 'its ends within the head block. Extending through the upper portion of the latch is a slot 59 for receiving a pin 60 threaded into an opening in the annular member 26 attached to the projection 2| on the rear motor head |0. Threaded into an opening 63 extending through the side of the head block 23 into the upper end of the chamber 56 is a plug 64 supporting a spring 65 for urging a plunger 66 inwardly through: the4 opening into engagement-J with a lateral .projection `61 formed on the latch. The feed screw extends `through the lower portionof the chamber 56, and surrounding the feed screw within this portion of Y the chamber is a sleeve member having inner `radially'extending projections 1| slidably fitting "within'j grooves12 in the feed screw. Formed in the outer'surface'of the sleeve member 10 are grooves 14 extending longitudinally of the feed screw and adapted to receive a lower hooked portion 15 of the latch 55 when it is swung in a clockwise direction, as viewed in Fig. 4, about its pivot pin 51. In order to holdv the sleeve member in a position beneath the latch 55, there is provided a split head 18 threaded into an opening 19 in the rear end of the boss portion 36 and having an annular groove 80 receiving a radially extendi'ng annular flange 8| on the rear end of the sleeve mem-ber.

During normalloads on the drill motor, the rear motor head ID is held against rotation in the bearings 22 relative to the rear` head block 23 by the Ispring pressed plunger 66 acting through the upper portion of the latch 55 against the pin 60. At the same time the latch 55 is held in a position so that its lower hooked portion is released from the grooves 14, and the feed screw is free to rotate. .On operating the handle 42 to rotate the feed screw. in aforward feeding direction, the feed nut 43 is caused to travel forwardly along the feed screw and force the spring 50 against the depending boss36 for moving the drill motor toward the material tov be drilled. If the load on the drill ,motor increases to a point where the rear motor head is caused to 'rotate in the bearings 22 against the force exerted by the spring 65, then the latch 55 will be caused to swingabout its pivot pin 51 until the lower hooked portion of the latch engages one of the grooves 14 in the sleeve member 10 and locks the feed screw against further rotation. The drill motor continues to be urged by the spring 50 in a forward feeding direction until the nut 46 on the forward end of the feednut is engaged by the front end of the bosslike portion 36. As soon as the load on the drill lmotor decreases to apoint where the spring 65 causes the rear motor head to turn in a clockwise direction, as viewed in Fig. 4, the latch 55 is released from the grooves 14 in the sleeve member 10 and the feed screw is freed for rotation.I

A modification of the feed screw locking means is shown in Figs. 6 and 7. The partsof the drill mechanism, other than the locking means, are the same as those described above and will be given like reference numerals. The feed screw locking means, generally designated 64, comprises an arm arranged within the chamber 56 and pivotally mounted between its ends on a pin 86 extending through the chamber parallel to the feed screw 31. Surrounding the portion of the feed screw extending through the chamber 56 is a sleeve member 81 having inwardly projecting portions 88 .slidably fitting within the'grooves 12 in the feed screw. Extending part way around the sleevemember 81 is a flexible friction band 90 having one of its ends xed to a pin 9| at- .endrof zthefarml. -At theupper end of-t-hefarm .8:5 eis a slot :.94 .receiving ithe pin 1li-ll yfprojecting reanWard-lyfrrom .the-'rearfmotorlhead ,-Hl. j :A lat-,- eral projection 135-onthe f(upper portion9j of the arm-. 35 isfengaged bythe-spring pressedsplunger .E6 for fholding therear motor fheadfagainstf-rotaf :tion in fthebearingsZZduringmormal motor loads,

lease -theebrake Aband lhfrem the -outer .surface cfu-the sleeve-member im. .Ata .predetermined maximum-.loaden thetdrilllmotor, the 'rear motor head t0 is caused :torrotate relative=-to ythe rear head block and swing the arm 85 faboutfits-pivot d against the .faction-of the .spring pressed-plunger .Bwpulling .the `:brake i band 9,0 about .the ,sleeve t member` :89 for braking the .rotation .of the lfeed screw.

fAsa ,resultothis `invention there-Jarefprovided ee.

improved.means ,forv controlling i the, feeding l'oa .drilling .tool .relative toits work. It `will.loe-noted vthat the forward. feedingfpressure Yvon theqdrilling tool .may .be `agradually .increased .until the load .onl-the.drillmotor.reachesafpredeterminedlmaxif2? wipmateriapto wbe drilled., meansjfopfeeding mumval-ue, Whenthemaximmn desired loadlon the ,drill.,motor .hasi been Y reached-.the feed mechanism is automatically lockedio rprevent a iure 4therincrease .in the Yforward =feeding fpressure.

the forward feeding pressure is transmittedgeto theldrilling tool, afeedingpressureis maintained .on-the',.dri1ling ,toolev,en.after .the `feed mechanism .is locked. .As .the .lload on .the lmotor .de-

creases, the feeding..mechanism..is `lautomatica'lfly 253i) releasedtolpermit `ahuilding uprof .the .feeding pressure again. .Due Lto fthe .subjection Aofwthe .drilling tool to .continuous "feeding pressure "sud:- "den, strains `on l,parts YAof .the .drill .mechanism are prevented and an improved .eiiiciencytof opera,- f tion lisolotainedl i 4 While Ihave in .this ,application specicallyde- Ascribed 4one "formand a modiiication ,Whichmy invention` may assume in practice, it` .willL be .understood Vthat this form and `I nojdicationare shown 'for purposes ...of illustration, Yand that the inventiony maybe further modiiied and embodied in various 'other forms without 4departingfrom its spirit or the scopeoftheappendedclaims. f H

jWhat'I claim 'as new andidesire to 'securehy Letters Patentis: -v 1, AIn .a drilling apparatus,` in ..comb`ination`, means 'for'.rotating a drilling implement for causi-` ing the sameto 'effect 'its drilling :function inclu'ding anfimplementerotating motor, means' fV `jfeeling adrilling implement which is. rotated by said `implement-rotating motor intothe'- workdir- 'ing "drilling, 'said `rfeeding means includingy ele'- ments cooperating on relative 'movement 'toj'provide 'a Vfeeding force 'and a yieldab'le `element 5.0

through which feeding pressures aredeliveredlto the-implement during drilling, said--yieldable yelement v"having a portion vthereof so 'operatively relatedto the1 implement tofbe'lfed, Aduringjdrill; in'g,A thatorward movements of lsueh portion vand of -the :drilling implement as the *latter is'fedare simultaneous and equal vin extent, "lan'd4 means responsive tofthe 'torque loads on said implement rotating meansand operative'at a predetermined maximum*torqueloadfforfautomatically prevent# v ing' further lincrease ifinthe 'feeding pressures transmitted 1 through isaidl yiel dable :element toth'e implement :for precluding ".the :application of iLan excessive :feeding :pressure Y to ltheimplement;f

l ?a drilling. aapparatus, combination;

means for rotatingmadrillingimplement-for^caus ing ,thesame` vtofeieet fits drilling .function including i `an 'fimplemen-tfiotatin'g motor, Ameans for feed-ins fafdrilling implement whihis 'rotated by1- said implement-rotating motorV into the y`work duringgdril'ling, said feeding means includingielements cooperating on relative "movement to-jpro- -vide a feeding force .andtyieldable means "for 0 transmittingthe feeding pressures toithefdrilling .andtformholdingathe arm/$815' insa position Vto ref i111 5 taneous-andf-equal inieictent, andfmeansfresponsive 4.to lthe itorgquef-.loads .pon l,said innalexnentrotating rmeans :for :automatically llimiting the feeding. pressuresv transmitted through :said yieldable means to the limplement for :precluding the application of al1-excessive -feeding pressure-,totheimplement 3u In ta `dri-11 mechanism, in combination, :a motor Vfor rotating a, drilling ytool,; meansY supporting-andguiding saidlmotor for movement rrelasaid motor along said 'support-mg and :guiding means, 1.a lyieldalole'@element through which 1ra forward feeding.pressure is transmitted zto lsaid g motorand.lmeans responsiyefto the=torque :loads `Byffreason. of..the yielding means through v.which f3.0

ing an increase in the feeding pressure'trans-V mittedz through said yieldablevelement. 4l In a .drill-mechanism, combination,` a motor -forfrotating fa-y .driliing ftool, means" supporting said motor ,for bodily-` movement relative to..ma.teria1-to.-be drilled :andfor limited rotary movement'grelative fto said supporting "means, 0 means,-.for feeding @said :motor relative to the material to be drilled, .lyieldable-means-for .transmittingtheieeding pressure .to said s'motor, `and means actuated by thei'frotary movement of .l said motor; lon said supporting zmeans for 4lin'iiting zthe 5 feeding pressure :applied fto said Vmotor v'transmittedwthrough.. saidl .yieldable transmitting .rneans.f p 1f i I5. .In a drill mechanism; einy combination, za motor for rotating a drilling tool, means .sup-

59 pontingsaid motor for:bodily:movementrrelative tofmaterialV toghe drilled-andiforlimited rotary movement-relative ato; said 7s1 ipnortin-g zmeans, meansior ,feeding said .motor relative-to the material -to-:be` driliedpayieldable element through ir l5 whiehafieedingmressure is'transmittedctosaid motor, and 1means' :actuated .by `the. .rotary movement1 of said motor on ysaid i supporting means n for .eontrollingithe feeding` pressures transmitted' through saidyieidable element tor said motor:

.-.6..,'In a dril1-mechanism, combination, `a motor for frotati-ng andri1lingtool,zmeans supporting said metoriior bodily movement relativeto material to .be drilled :and for rlimite'd Vrotary movement relative to ,':s'aid supporting vmeans,

g5 meanswfor feeding said-motor relativewto the materialto be :drilledfayieldable element; through which a feeding pressure is transmitted tosaid motor, .and means actuatedV Aby. the -rotary'linovementy of saidmotoraon said-supporting means `.at

a,predetermined maximum motor .load lforgprevrenting-fan increase-in the feedirijgpressurel transmitted throughfsaid `yieldalele element. -7.,In.1,a\-drilling-;,apparatus, iin .-combination, means `for lrotatingf-.amdrilling :implement for 35 causing .the same-to :eiectlitsdrillingriunction including an"implementrotating motor, means for feeding a drilling implement which is rotated by said implement-rotating motor toward the work during drilling including relatively rotatable feeding elements coolieratin-g-pnv relative rotation to provide a feeding force and: yieldable means for transmitting feeding pressures to the implement on relative rotation of said feeding. elements, said yieldable means having a portion thereof so operatively related to the implement to be fed, during drilling, that forwardmovements of such portion and of the drilling implement as vthe latter is fed are simultaneous and equal in extent, and means responsive to the torque loads on said motor for automatically controlling the relative rotation of said feeding elements for precluding thetransmission of an excessive feeding pressure through said yieldable means to the implement.

8. In a drill mechanism, in combination, a motor for rotating a driling tool, means supporting and guiding said motor for movement relative to material to be drilled, means including relatively rotatable elements for'feeding said motor along said supporting and guiding means, yielding means for transmitting feeding pressure to said moto-r on relative rotation of said elements, means for rotating one of said relatively rotatable elements, and means operative at a predetermined maximum Iload on said motor for locking the last mentioned one of said elements against rotation. 1

9. In a drill mechanism,`in combination, a motor for rotating a drilling tool, means supporting and guiding said'motor for bodily movement relative to material t'o be drilled, means for feeding said motor along 'said supporting and guiding means, saidfeeding means "including la feed nut operatively connected to said motor for rectilinear movement relative to the latter,`a feed screwv threadedly engaging said feed nut and feedingmeans including a feed nut operatively connected to said motor for yrectilinear movement relative to the latter, a feed screw threadedly engaging said feed nut and means for rotating said feed screw, and means operative on the rotation of said motor at a predetermined maximum load for locking said feed screw against rotation, said feed'screw locking means including a latch operatively connected to said motor and mounted for pivotal movement relative to the latter, and a member fixed against angular movement relative to said feed screw and adapted to be engaged by said latch on pivotalA movement of the latter for locking said feed screw against rotation. l

1'2. In a drilling mechanism', in combination, means providing a guideway, a drilling `motor mounted for sliding movement on said guide'- way-providing means, relatively rotatable members, one movable along said guideway with the drilling motor'and one mounted onfsaid guideway-providing means, foreflyecting feeding of saiddrilling motor along said guideway on relative rotationfbetween them, a yieldingpressuretransmitting connection between said member movable along said guideway with said drilling motor and said drilling motor, and means governed by the resistance to drilling for precluding relative rotation between said members while resistance to drilling exceedsa predetermined amount. Y J.

13. In a drilling mechanism, in combination, means providing a guideway, a drillingmotor mounted for sliding movement on said guideway-providing means, relatively rotatable members, one movable along said guideway with the drilling motor and one mounted on said guideway-providing means,'for effecting feeding of means for rotating said. feed screw, yielding o meansbetween said motor and said feed nut for resisting rectilinear movement of said feed nut in a forward direction relative to said motor, and means operative at a predetermined load on said motor for lockingsaid feed screw' against rotation, i

10. In a drill mechanism, in combination, a motor for rotating a drilling tool, meansv supporting and guiding said motor :for bodily movement relative to material to be drilled, said supporting and guiding means permitting relative angular movement of said motor at predetermined loads on the latter, means for feeding said lmotor along said supporting and guiding means, `said feeding means including a feed nut operatively connected to said motor for rectilinear movementrelative to the latter, a feed screw threadedly engaging said feed nut and means for rotating said feed screw, yielding means for transmitting feeding pressure from said feed nut to said motor, and means operative on the angular movement of said motor at a .predetermined maximum loadfor locking said feed screw against rotation.

1l. In a, drill mechanism, in combination, aY

motor for rotating a drilling tool, means supporting and guiding said motor for Abodily movement relative to material to be drilled, said supporting and guiding means permitting relative angular movement of said motor at predetermined loads on the latter, means for feeding said motor along said supporting and guiding means, 'said said drilling motor along said guideway on relative rotation between them, means yielda'bly connecting the one of said members which is movable with said. drilling motor with the latter providing for relative movement between said motor and said member in a direction longitudinal of said guideway, and means governed'by the resistance to drilling for precluding relative rotar tion between said members while resistance to drilling exceeds a predetermined amount, said last mentioned means including alock. for locking against rotation the rotatable one of said members. f

14. In a drilling mechanism, in combination, means providing a guideway,. a drilling motor mounted for sliding movement on said guidewayproviding ineans, relatively rotatable members, one movable along said guideway with the drilling motor and one mounted on said guideway-providing means, for effecting feeding of said drilling motoralong said guideway on relative rotation between them, vmeans yieldably connecting the one of said members which is movable` with said drilling motor with the latter providing for relative movement between said motor and said member in a direction longitudinal of said guideway,

and means governed by the resistance to drilling the material to be drilled, means for mounting said motor for limited yielding movement relative to said supporting means, means for feeding said motor relative to the material to be drilled, yieldable means other than said yielding mounting means for transmitting the feeding pressure to said motor, and means actuated by the limited feeding force providing means for feeding a drilling implement actuated by said implement-actuating means toward the work during drilling, means providing a yielding connection between said feeding force providing means and .the implement for yieldingly transmitting-the feeding pressures to the implement, said means providing a yielding connection having a portion thereof so operatively related to the implement to be fed, during drilling, that forward movements of such portion and of the drilling implement as the latter is fed are simultaneous and equal in extent, motion-checking means for regulating the feeding pressures transmitted by said feeding force providing means through said yielding connection to the implement, and means responsive to the load changes on the implement for automatically regulating said motion-checking means to limit the feeding pressures transmitted to the implement through said yielding connection for precluding the application of' an excessive feeding pressure to the implement.`

17. In a drilling apparatus, in combination, means for actuating a drill bit, feeding force providing means for a drill bit actuated by said actuating means including relatively rotatable kcoacting feeding elements, means providing a yielding connection advanced with the bit during forward feeding and between said feeding force providing means and the drill bit which is fed thereby whereby the feeding pressures are yieldingly transmitted to the drill bit, said yielding connection providing means having a portion thereof so operatively related to the drill bit, during drilling, that forward movements o-f such portion and of the drill bit as the latter is fed are simultaneous and equal in extent, and means automatically responsive to torque-load changes on said bit actuating means forregulating the rate of relative rotation between said feeding elements to vary the feeding pressures transmitted to said yielding connection.

18. In a drilling apparatus, in combination, means for actuating a drilling instrumentality for causing the same to effect its drilling function, feeding force providing means for applying feeding pressures to a drilling instrumentality for urging the latter toward. the work as drilling proceeds, yielding-pressure-transmitting means moved bodily in the feeding direction to effect feeding v and whereby the feeding pressures are yieldingly applied to said drilling instrumentality, said yielding pressure transmitting means having a portion thereof so operatively related .to the instrumentality to be fed, during drilling, that forward movements of such portion and of the drilling instrumentality as the latter is fed are simultaneous and equal in extent, and means for regulating said feeding force providing means t-o limit the feeding pressures applied to such instrumentality through said yieldable-pressure-transmit- `ting means automatically in accordance with torque load changes on the instrumentality for precluding the application of an excessive feeding pressure to the instrumentality.

19.1n a drilling apparatus, 'in combination,

' means for actuating a drilling instrumentality for causing the same to effect its drilling function, feeding force providing means for applying feeding pressures to a drilling instrumentality actuated by said actuating means for urging such instrumentality toward the work as drilling proceeds, means advancing With the drilling instrumentality during feeding for yieldingly transmitting the feeding pressures from said feeding force providing means to `the instrumentality, said means for yieldingly transmitting the feeding pressures having a portion thereof so operatively related to the instrumentality to be fed, during drilling, that forward movements of such portion and of the drilling instrumentality as the latter is fed are simultaneous and equal in extent, and means responsive to torque load changes` on the instrumentality for automatically varying the ef- -fectiveness of said feeding means whereby the feeding pressures transmitted to the instrumentality through said yielding transmitting means are automatically limited.

' WIN vv. PAGET. 

